With the development in a display technique, an organic light emitting diode (OLED) display apparatus has become one of popular display techniques because of its advantages such as simple manufacture process, thinner product, high light brightness, fast response speed, low cost, low operation temperature, etc.
According to different driving manners, the OLED display apparatus can be divided into a Passive Matrix Organic Light Emission Display (PMOLED) and an Active Matrix Organic Light Emission Display (AMOLED). As compared with the PMOLED, the AMOLED has a faster response speed and can satisfy requirements for various sizes of the display apparatus. Therefore, many companies focus on the AMOLED more.
As an original pixel driving circuit for the AMOLED, a structure of a 2T1C pixel driving circuit comprises, as illustrated in FIG. 1, a driving transistor DTFT, a switch transistor T1, an organic light emitting diode OLED and a storage capacitor Cs. When a row is scanned, a scan voltage Vscan is at a low potential, the switch transistor T is turned on, and a data voltage Vdata charges the storage capacitor Cs; when the scanning for this row is completed, the scan voltage Vscan turns to be at a high potential, the switch transistor T is turned off, and the storage capacitor Cs discharges, so that the driving transistor DTFT is in a saturation conduction state, and generates a current to drive the organic light emitting diode OLED, thus ensuring that the organic light emitting diode OLED emits light continuously during a frame of picture.
According to a formula for calculating a leakage current of the transistor, operating current IOLED of the organic light emitting diode OLED satisfies an equation as follows: IOLED=K(VGS−Vth)2, wherein VGS is a voltage difference between a gate and a source of the driving transistor DTFT, and Vth is a threshold voltage of the driving transistor DTFT. Because differences in the processes for different TFTs and other factors such as aging caused by applying a voltage or a high temperature for a long time, and the like, the threshold voltages Vth of the driving transistors DTFTs in different pixel points may shift, such that the current (namely the operating current IOLED) flowing through the organic light emitting diodes OLEDs in the respective pixel points becomes inconsistent with each other due to the shifting of the threshold voltage Vth, the brightness at the respective pixel points are different in the display apparatus, and finally a display effect of an entire picture is affected.